During the third year of our project we hope to extend our knowledge of syngeneic host-tumor interactions. The UV-tumor model has provided us with an easy way to manipulate a syngeneic system so that either an effector or suppressor mechanism will dominate following tumor challenge. This provides a potential means of investigating numerous questions about immunoregulatory influences and effector cell responses. We propose to study the nature of the effector T-cell-suppressor T-cell interaction and to acquire knowledge of the lymphocyte and macrophage subpopulations necessary to generate the antitumor immune state. Tumors will be evaluated with respect to the various types of membrane-bound antigens they possess (both TSTA and TAA). The immunologic responses (effector and regulatory) will be studied as they relate to these tumor antigens.